The public Play() method doesn't seem to work. Pls could some one help me.

A constructor must be named the same as the class. The compiler does not recognize Play as a constructor because it is not named appropriately. It therefore presumes it to be a method, but missing a return type -- causing the compilation error.

How do i make it that when i die the counter stops. I have tried putting Greenfoot.stop(); but this doesn't get rid of the entire health bar but it stops everything. This is where the Greenfoot.stop();

How exactly does that work. Like it says public void stop and then running = false; so how do i change it into when i die it stops. whats the code

How do you think it works? It is always the same when you tell an object to do something:
(pseudo-code) object.doSomething();
Sometimes the object is missing, but then it is implicitly given:
(pseudo-code) doSomething();
which is equivalent to:
(pseudo-code) this.doSomething();
Just like a command -- subject followed by verb.